1. Field of the Invention
This invention relates to a control system for an automatic vehicle transmission.
2. Description of the Related Art
As a typical prior-art control system for automatic vehicle transmissions, Japanese Laid-Open Patent Application No. Hei 6 (1994)-341525 teaches detecting over-revving of the engine and tie-up of the frictional engaging element such as a hydraulic clutch and when it is detected that the engine revs over or excessively, changing the characteristics of control to raise the pressure of the clutch to be engaged, to make the slope steep in the wave-form of supplied pressure or to quicken the timing to raise the pressure, thereby suppressing the shift shock due to over-revving of the engine or clutch tie-up.
Since, however, the performance of tracking or follow-up of hydraulic pressure is not taken into account in this prior art, the engine may rev over when the engine torque is increased. In other words, the control toughness against the engine speed is not satisfactory in the prior art.
Aside from the above, when determining the pressure to be supplied to the frictional engaging element such as the clutch, as taught by Japanese Laid-Open Patent Application No. Hei 7 (1995)-151222, in view of the fact that the friction coefficient xcexc of the clutch varies depending on the temperature of the pressurized oil (ATF), i.e, the viscosity of oil, the pressure to be supplied is corrected by the friction coefficient so as to determine the pressure appropriately, thereby decreasing the shift shock experienced by the vehicle occupant.
Since, however, the friction coefficient of the clutch changes not only by the oil viscosity, but also by the rotational difference of the clutch, it is preferable to calculate the clutch friction coefficient taking other parameters including the clutch rotational difference account.
An object of this invention is therefore to overcome the aforesaid problems and to provide a control system for automatic vehicle transmission, which determines the hydraulic pressure to be supplied to the frictional engaging element such as a hydraulic clutch, taking the performance of tracking or follow-up of the hydraulic pressure into account, to enhance the control toughness against the engine speed change, thereby decreasing the shift shock effectively so as to improve the feeling of the vehicle occupant, while ensuring to prevent the engine from revving over or excessively.
Another object of this invention is therefore to overcome the aforesaid problems and to provide a control system for automatic vehicle transmission, which calculates the friction coefficient of the frictional engaging element such as a hydraulic clutch additionally taking parameters including the rotational difference thereof into account to determine the pressure to be supplied to the frictional engaging element, thereby decreasing the shift shock effectively so as to improve the feeling of the vehicle occupant.
In order to achieve the objects, in a first aspect, there is provided a system for controlling an automatic transmission of a vehicle having an input shaft connected to an internal combustion engine mounted on the vehicle and an output shaft connected to driven wheels of the vehicle, the transmission transmitting input torque, through any of frictional engaging elements, generated by the engine and inputted by the input shaft to the driven wheels by the output shaft, in accordance with predetermined shift scheduling defining a target gear based on detected operating conditions of the vehicle and the engine, comprising; input shaft rotational speed detecting means for detecting input shaft rotational speed inputted to the transmission; input torque calculating means for calculating the input torque inputted to the transmission; reached-pressure determining means for determining a reached-pressure based on at least the calculated input torque; maximum control response value determining means for determining a maximum value in pressure control response set with respect to a desired reaching time in accordance with a predetermined characteristic, based on at least the detected input shaft rotational speed and the determined reached-pressure; actual control response value determining means for determining an actual value in the pressure control response based on at least the determined reached-pressure relative to the desired reaching time; desired value determining means for comparing the determined maximum value and the determined actual value to determine the pressure control response and for determining a desired value to be supplied to one of the frictional engaging elements of the target gear to be shift to, based on the determined pressure control response; hydraulic pressure calculating means for calculating hydraulic pressure to be supplied to the one of the frictional engaging elements based on the desired value; and hydraulic pressure control circuit for supplying hydraulic pressure to the frictional engaging elements based on at least the calculated hydraulic pressure.
In a second aspect, there is provided a system for controlling an automatic transmission of a vehicle having an input shaft connected to an internal combustion engine mounted on the vehicle and an output shaft connected to driven wheels of the vehicle, the transmission transmitting input torque, through any of frictional engaging elements, generated by the engine and inputted by the input shaft to the driven wheels by the output shaft, in accordance with predetermined shift scheduling defining a target gear based on detected operating conditions of the vehicle and the engine, comprising; input shaft rotational speed detecting means for detecting input shaft rotational speed inputted to the transmission; output shaft rotational speed detecting means for detecting an output shaft rotational speed to be outputted from the transmission; temperature detecting means for detecting a temperature of oil generating the hydraulic pressure; viscosity parameter calculating means for calculating a viscosity parameter indicative of viscosity of the oil based on the detected temperature of the oil in accordance with a predetermined characteristic; desired torque calculating means for calculating a desired torque necessary for effecting shift to be supplied to one of the frictional engaging elements of the target gear; surface pressure calculating means for calculating a surface pressure acting on the one of the frictional engaging elements based on at least the desired torque; clutch parameter calculating means for calculating a clutch parameter indicative of condition of the frictional engaging elements based on at least the calculated viscosity parameter, the surface pressure, the detected input shaft rotational speed and the detected output shaft rotational speed; friction coefficient calculating means for calculating a friction coefficient of the frictional engaging elements based on the calculated clutch parameter in accordance with a predetermined second characteristic; conversion means for converting the desired torque into the hydraulic pressure value using at least the calculated frictional coefficient and. hydraulic pressure control circuit for supplying the calculated hydraulic pressure to the one of the frictional engaging elements based on at least the calculated hydraulic pressure.